They're trying to force the workers to strike so they can make their case to the government that the strike is disrupting an essential service and demand that they force the union to accept the terms. Literally the same thing happened a year ago: Postal workers make demands and are willing to negotiate, Canada Post completely refuses to negotiate and locks out the workers, workers strike, postal traffic in Canada grinds to a halt, millions of people and businesses are impacted, Canadian government cites the post office as an "essential service" and uses that to force the union and employer into arbitration even though the employer was the belligerent one and didn't even attempt to negotiate in the first place.

Also, news outlets scapegoated the union for all the delayed mail the last time they went on strike. "How could they do this to Canada? Can't they just accept working like slaves? It's an essential service after all, that means we get to exploit the people doing the job as much as we want and if they strike they're the problem!" No mention of what the union's actual demands were or how the post office itself acted.

Also also, Canada Post is NOT tax funded. It's a government institution that is set up like a normal corporation, but with the government as the shareholder. If that's not an ass backwards way of providing an essential service I don't know what is. Literally the worst of both worlds between private and public ownership.